Variation in Sterilization Cycles: The continued need for load monitoring devices.

OVERVIEW BACKGROUND: BIOLOGICAL INDICATORS, CLASS 5 INDICATORS AND CLASS 6 INDICATORS DEFINED A TYPICAL STERILIZER CYCLE AND HOW THIS DIFFERS FROM INDICATOR VALIDATION CONDITIONS REAL WORLD EXAMPLES AND THE NEED FOR LOAD MONITORING: (1) STERILIZER MALFUNCTION, (2) STERILIZER SETTINGS AND (3) STERILIZER IDIOSYNCRACIES

The question we’re hearing more and more frequently: If my indicator passed a minute or two into the exposure phase ---- THEN WHAT GOOD IS IT? Background: Biological Indicators, Class 5 and Class 6 Indicators.

Class 5 integrators are intended to mirror the death curve of the Geobaccilus Stearothermophilus bacteria with a margin of safety. Note that this statement is only true with respect to naked BI strips. There is no correlation between a Class 5 and a self contained biological indicator. Class 5 vs. Class 6 Indicators Background: Biological Indicators, Class 5 and Class 6 Indicators.

Class 6 emulators vs. Class 5 integrators. At a given cycle point, a Class 6 emulator provides significantly more resistance to the sterilization process than a Class 5 integrator and thus is a more effective load monitoring device.  ISO standard for Class 6 is that the indicator must pass at the stated value and must fail at -1°C and -6% time.  ISO standard for Class 5 is that the indicator must pass at the stated value and must fail at stated value temperature and 63.6% of stated value time.  Typically the stated value for a Class 5 at 134°C is approx. 2 minutes. The stated value for a Class 6 at 134°C is 3.5, 4 minutes or longer depending on the cycle in question.  At 134°C, a Class 6 has at least twice the stated value and has a 2.5 times tighter tolerance. vs. Background: Biological Indicators, Class 5 and Class 6 Indicators.

A Class 6 indicator provides a much more significant test to sterilizer efficacy than a Class 5 INDICATOR 134°C 4 MINUTES 133°C 3.76 MINUTES 134°C 3.5 MINUTES 133°C 3.29 MINUTES CLASS 6PASSFAILPASSFAIL CLASS 5PASS Background: Biological Indicators, Class 5 and Class 6 Indicators.

PER ISO (STANDARD GOVERNING INDICATOR PERFORMANCE) CHEMICAL INDICATORS ARE VALIDATED IN BIER (BIOLOGICAL INDICATOR EVALUATION RESISTOMER) VESSELS. EXPOSURE CONDITIONS IN BIER VESSEL DIFFER GREATLY FROM THOSE IN STERILIZER:  One pre-vacuum pulse is pulled. Phase cannot exceed 2 minutes.  Exposure temp is achieved in less than 10 seconds  One exhaust vacuum is pulled. Phase cannot exceed 1 minute.  Temperature tolerance of +/- 0.5°C Typical sterilizer cycle vs. Indicator validation conditions.

ANSI / AAMI / ISO B-1 CYCLE

ANSI / AAMI / ISO B-2 CYCLE

MOST STERILIZER CYCLES ARE A HYBRID OF THE B-1 AND B-2 CYCLES, WHERE A DEEP VACUUM (E.G. 70 MILLIBARS) IS PULLED BUT THERE ARE ALSO SIGNIFICANT POSITIVE PRESSURE PULSES (E.G MILLIBARS) ALTERNATING WITH EACH VACUUM PULSE.  Multiple vacuum pulses. Total duration of minutes, with temps oscillating between 100°C-130°C (compared to one short pre-vac pulse).  Exposure temp is achieved in as much as 5-7 minutes after last vacuum pulse (compared to less than 10 seconds).  One exhaust vacuum is pulled, with dry phase lasting minutes (compared to 1 minute or less).  Exposure temp often exceeds setting by 1.5°C + (compared to temperature tolerance of +/- 0.5 C).  While the pre-vac phase might do a lot of the heavy lifting towards changing an indicator, a passed indicator means that adequate conditions were achieved wherever the indicator was placed (in a pouch, tray, pack, PCD etc.). Typical sterilizer cycle vs. Indicator validation conditions.

Real World Examples: Sterilizer Malfunction

10 inHg vacuum (approx 300 millibars) Normal setting is 28 inHg (approx 7o millibars) Real World Examples: Sterilizer Malfunction

Real World Examples: Sterilizer Settings

TimeTemp in °CPressure in millibars 08:36: :38: :38: :39: :39: :40: :40: Real World Examples: Sterilizer Settings

What went wrong? Come up time is way too fast. ISO sets upper limit for come up time at 250kpa/min or 42mbar/second. This sterilizer had a come up time of 67mbar/second or 60% over the upper limit established by the norm. Most sterilizer manufacturers set their come up time to around 10mbar/sec to ensure adequate air removal and lethality. TimeTemp in CPressure in millibars 08:36: :38: :38: :39: :39: :40: :40: Real World Examples: Sterilizer Settings

Pass result indicated by machine, fail result indicated by indicator. Real World Examples: Sterilizer Settings

Vacuum level of 60kpa Machine indicates “Pass” Real World Examples: Sterilizer Settings

Vacuum level of 60kpa 60 kpa (or approx 600 millibars) ISO calls for an initial pulse to 5kpa and then additional pulses with at least a 50kpa vacuum depth, depending on cycle (sub-atmospheric, trans-atmospheric or super-atmospheric). When we validated for the ISO norm, we set the fail cycle at 250 millibars deeper than the setting on this machine. Inadequate vacuum can result in residual air inside of pouches, packs and trays. Real World Examples: Sterilizer Settings

We have seen about a 40% drop in efficiency in sterilizers that idle for more than 60 minutes. True across sterilizer brands. Our test was conducted on a major brand, a customer validated on another major brand. Harborview Med Ctr (Univ of Washington Medicine): “I … ran three tests side by side, one that had been idle for 30 min one that was idle for 60 min and one that wasn't idle at all and I found that all three tests with the 60 min idle had positive BIs. So it was logical to conclude that there was a drop off in efficiency that had to be corrected for prior to using the devices for loads.” These results make sense and don’t mean that the sterilizers are malfunctioning. On the first cycle after extended idle time, energy is expended heating sterilizer chamber walls, which has a deleterious effect on sterilizer efficiency. Exposure TimeIdle TimeTemp in °CBI Survival Rate 4 minutes75 minutes13297% 4 minutes15 minutes13250% Real World Examples: Sterilizer Idiosyncrasies INCONSISTENT STERILIZER PERFORMANCE DUE TO FLUCTUATIONS IN IDLE TIME

 Sterilizer exposure conditions differ greatly from validation conditions inside of a BIER vessel. While the pre-vac phase might do a lot of the heavy lifting towards changing an indicator, a passed indicator means that adequate conditions were achieved wherever the indicator was placed (in a pouch, tray, pack, PCD etc.).  At a given cycle point, a Class 6 indicator is significantly more resistant than a Class 5 indicator.  There is wide variation in sterilizer performance, due to a number of potential factors: (1) malfunction, (2) settings or (3) idiosyncrasies. Occurrences falling under categories (2) and (3) in some ways pose the greatest risks because, on the surface, everything seems to be working, and these cannot be detected by calibrations / preventive maintenance.  Load monitoring devices are validated to norms. A good load monitoring device should act as a constant amidst the many variables that are involved in sterilization by enabling the CSSD professional to compare sterilizer performance to the baseline performance established by the applicable norm. Lessons